Oil wells are generally formed by drilling a bore into the earth for accessing buried crude oil deposits, and then installing a variety of equipment within the bore to enable pumping of crude oil up to the earth's surface. During drilling, hollow metallic tubes (also known as ‘casings’) are inserted within the bore to prevent walls of bore from collapsing. In a deep enough bore, multiple hollow casings are installed vertically one above the other by screwing ends of adjacent sections with each other. The entire assembly of attached casings is commonly known as ‘bore casing’.
Once a bore casing is formed, a variety of equipment (including crude oil pumping equipment and sensor equipment) is installed within the bore casing. In an operational oil well, crude oil is pumped to the surface of the earth from the buried crude oil deposits with the help of pumping equipment installed in the bore casing.
Performance and efficiency of an oil well production unit is vulnerable to failure of equipment installed within bore casing, or changed conditions within the well bore. Troubleshooting of such problems often requires liberating (or setting free) stuck equipment or retrieval (or fishing) of equipment within the bore casing.
Liberation of a stuck equipment or its retrieval is often performed with coiled tubing, which rides out on a powered drum and down the bore casing. The coiled tubing often includes a drilling jar which is capable of providing a striking impact (or a shock wave) in both upwards and downwards directions, in order to free trapped equipment or tubing sections. See U.S. Pat. No. 8,151,910 (incorporated by reference). In an attempt to free stuck equipment or to separate it from the installed equipment assembly, the jarring device generates a striking impact which in turn generates a shock wave along the coil tubing, which travels to the stuck equipment.
Often, installed equipment within a well bore casing is held together by interlocking friction fittings. For successful separation of such installed equipment assembly, it is important that the jarring impact is strong enough to overcome resistance from such friction fittings.
Though currently known jarring devices claim to facilitate separation of desired equipment within a bore casing, their jar (or strike) generating mechanisms are often too weak to be effective. U.S. Pat. No. 8,151,910 (the '910 patent) discloses a jarring device which generates jarring impact by exerting either stretch or compression loading forces on a mandrel, followed by sudden release of the fluid pressure resisting either of these loading forces. However, in the jarring device of the '910 patent, the fluid continually leaks out of the region of resistant fluid compression during exposure to the loading forces. The resistant force is therefore reduced by leakage, and as a result, the jarring impact generated is weakened.